Transponders are well known in the general field of security systems.
The use of transponders in this field generally concerns Remote Keyless Entry (RKE) systems. An interrogator circuit is used as a lock and a separate transponder circuit is used as a key. The interrogator circuit transmits a question signal, usually a Radio Frequency signal, that is received by the transponder. The question signal is then modified by the transponder according to a predetermined pattern to generate a response signal that is transmitted from the transponder back to the interrogator circuit. Upon receipt of this response signal, the interrogator circuit compares the received response signal with a stored expected response signal. If the comparison is accepted, the interrogator circuit generates an output signal to deactivate a mechanical lock or any other mechanism electrically connected to the interrogator circuit.
Improvements have been made in these RKE systems to provide keys that do not require power sources, i.e. batteries. In these cases, a portion of the energy of the received question signal is rectified by a rectifier circuit and stored in an energy storage element, usually a capacitor, to provide the required electrical energy to generate the response signal and to transmit this response signal.
A major drawback common to the transponder systems used as RKE systems concerns the constant powered on state of the interrogator circuit. This drawback is not so great when the interrogator is connected to the electrical power grid. However, when the interrogator circuit is used in a battery operated environment such as, for example a motor vehicle (an automobile, a snowmobile, an all-terrain vehicle, a boat, a personal water craft . . .) it is obviously not interesting to leave the interrogator circuit constantly energized.
Safety systems for vehicles using a kill switch automatically triggered when the driver of the vehicle is ejected from the vehicle are also generally well known. Usually, a lanyard links the driver to a mechanical switch that is automatically placed in an open position should the lanyard be disconnected from the switch. Such safety systems are often found on water crafts such as boats and personal water crafts, but could also be used on all-terrain vehicles, snowmobiles or other vehicles where the driver could be ejected.
U.S. Pat. No. 6,352,045 issued to Takashima and entitled “Immobilization system for watercraft” describes a transponder system used on a watercraft as a RKE system. Takashima's system also includes a conventional lanyard safety system provided with a mechanical kill switch to which an end of the lanyard must be connected for proper operation of the vehicle. The key of the transponder system is necessary for the ignition of the engine of the vehicle and the lanyard system is necessary for the continuing operation of the engine.
Canadian Patent application 2,206,286 published on Nov. 27, 1998 and entitled “Transponder System” describes a transponder system using a reed-switch and corresponding magnet to both energize the interrogator circuit and as a safety system. Indeed, the magnet is embedded in the key that is linked to the driver via a lanyard cord.